Prostate cancer (CaP) is the most common malignancy in U.S. males, with over 300,000 new cases per year and almost 50,000 deaths per year. Identification of novel diagnostic markers and therapeutic targets for both incident and advanced CaP is a major goal of current research. First introduced in 1987, the serum level of prostate-specific antigen (PSA) remains the standard for non-invasive prostate cancer screening, with a level of 4.0 ng/ml being the currently accepted cut-off for referral for biopsy. A main source of concern with PSA measurements per se is the sensitivity of PSA assays versus their specificity, i.e., increased PSA levels that are due to factors other than prostate cancer, such as benign prostatic hyperplasia (BPH), prostatitis, etc. This is reflected by the fact that the ability of PSA to distinguish benign from malignant conditions is substantially better at concentrations above 10 ng/ml. Thus, the accurate characterization of cancer risk in patients in the so-called "gray zone" of 4-10 ng/ml requires an improved screening tool to prevent unnecessary diagnostic procedures. This need is reinforced by the presence of disseminated disease in 30% of men with PSA values in this range. An alternative approach would be the development of a multiplex assay that would measure a defined set of serum analytes that, together, would provide the basis for a robust algorithm for assessing CaP risk with single serum samples. We have initiated such an approach by identifying genes encoding secreted proteins that are uniquely up-regulated in CaP. We propose that the products of these genes will be present at elevated levels in the serum of men with CaP, and that these proteins represent a set of candidate biomarkers that can be exploited for the development of a sensitive and specific CaP screening tool. We will address this hypothesis in 2 specific aims. Aim 1 will determine the normal variation in an initial set of 20 candidate CaP biomarkers using antibody arrays and ELISA assays. Aim 2 will use a larger cohort that includes high-PSA, biopsy-positive and negative samples in an unblinded study to assess the efficacy of a smaller biomarker set to distinguish normals and biopsy- negative from CaP samples. These studies will provide the foundation for Phase-ll validation in a larger sample set and the identification of markers associated with disseminated, metastatic and androgen- independent disease, the improved diagnosis of which would also be of significant clinical utility. [unreadable] [unreadable] [unreadable]